This invention is in the field of ultrasonic visualization systems.
In a typical reflection ultrasonic display utilizing a series of B-mode lines, an acoustic pulse is directed at a target or specimen and the returning echoes received are displayed along the scan line. The fundamental frequency of the transmitted pulse is typically in the one megahertz to ten megahertz range. The resulting echoes (r.f.) are detected and the detected (video) signal utilized to produce a display such as on a storage oscilloscope or scan converter where each line is displayed and stored sequentially to produce a two dimensional view.
A typical Z-axis, or brightness, sensitivity range for an oscilloscope display might be from a 1 volt saturation level to a 0.1 volt minimum detected voltage to produce an indication on the screen. The ultrasonic reflection from a glass target might be as high as 20 volts while the reflection from a biological target might be as low as 20 microvolts. This 120 decibel difference in received voltage cannot be directly displayed on the scope whose full range is only 20 decibels. The alternatives heretofore utilized have been compression of the range of received voltages, rendering differences in intensity impossible to distinguish, and selection of a pair of thresholds above the 0.1 volt minimum received voltage and below the 1 volt maximum received voltage. In this case, where the received voltage exceeds the selected full brightness voltage for the oscilloscope, a large area of the screen will be illuminated, while for other reflections below the selected threshold no indication will be displayed of received ultrasound.